1. Field of the Invention
The present invention relates to a method for discriminating the sorts of optical discs. Also, the invention relates to an optical disc apparatus which is furnished with a method for discriminating the sorts of optical discs.
2. Description of Related Art
In late years, DVDs (Digital Versatile Discs: multipurpose discs) have come into wide use. Recently, in order to further increase the information quantity of an optical disc, researches on the higher density of the optical disc have been made, and an optical disc heightened in density, such as HD-DVD (High Definition DVD: high density DVD), has also appeared.
The record and reproduction of the information of an optical disc are performed in an optical disc apparatus. Optical disc apparatuses each of which can record and reproduce information onto and from a plurality of sorts of optical discs by the single apparatus have been developed in large numbers, and the optical disc apparatus which copes with the two sorts of optical discs of the DVD and the HD-DVD has also been proposed. Besides, in such an optical disc apparatus coping with the plurality of sorts of optical discs, when the optical disc is inserted into the apparatus, the sort of the optical disc is first discriminated.
Various methods have heretofore been proposed as methods for discriminating the sorts of the optical discs, and they are, for example, discrimination methods introduced in JP-A-2006-134367 and JP-A-2000-311357. According to the methods, a laser beam is projected, and an objective for condensing the laser beam onto an optical disc is moved in the direction of an optic axis, so as to obtain a focus error signal (FE signal) on this occasion. In addition, the sort of the optical disc is discriminated on the basis of the generation timing of the S-shaped waveform of the FE signal, the amplitude thereof, etc.
However, when the DVD and the HD-DVD are to be discriminated in accordance with the method stated in JP-A-2006-134367, that is, on the basis of the generation timing of the S-shaped waveform of the FE signal, the generation timings of the S-shaped waveforms of the DVD and the HD-DVD become the same for the reason that both the thicknesses of transparent cover layers for protecting record layers are equal to be 0.6 mm, in the DVD and the HD-DVD. Accordingly, the discrimination between the DVD and the HD-DVD becomes difficult.
Besides, in the configuration wherein the optical discs are discriminated by utilizing the magnitude of the amplitude of the S-shaped waveform as stated in JP-A-2006-134367 or JP-A-2000-311357, a plurality of sorts of wavelengths need to be changed-over for the laser beam which is projected onto the optical disc in order to discriminate the sorts of the optical discs. In this regard, a time period expended on the discrimination of the optical disc becomes long in some cases, for such a reason that, in changing-over the sorts of the wavelengths of the laser beam, a wait time is required until the output of a laser beam source is stabilized. In this respect, the wavelengths of the light sources which are used for the DVD and the HD-DVD are different (for example, 650 nm for the DVD, and for example, 405 nm for the HD-DVD), and the optical disc apparatus which can record and reproduce information for the DVD and the HD-DVD has the problem that a long time is expended on the discrimination between the DVD and the HD-DVD.